GENEVA (AP) — Almost everyone in large cities in poor and middle-income countries faces excessively high air pollution, a growing problem that is killing more than 3 million people prematurely each year and “wreaking havoc on human health,” the World Health Organization said Thursday.

The U.N. health agency says more than four out of five city dwellers worldwide live in cities that don’t meet WHO air quality guidelines – 98 percent in poorer countries and 56 percent even in high-income countries.

“Ambient air pollution, made of high concentrations of small and fine particulate matter, is the greatest environmental risk to health, causing more than 3 million premature deaths worldwide ever year,” WHO said.